New discoveries about insect nanostructure, like a mosquito’s eye, could help design improved water-repellent coatings. Credit: Ling Wang, Penn State
Researchers have theorized that a coating that mimics the unique nanostructure could enhance virus-repellent face masks.
Through research on insect surfaces, Penn State researchers have detailed a previously unidentified nanostructure that can be used to design stronger, more resistant water-repellent coatings.
The results of this research were published today (July 17) in Progress of science.
With an improved ability to repel droplets, this design could be applied to personal protective equipment (PPE) to better resist virus-laden particles, such as COVID-19, among other applications.
“For the past few decades, conventionally designed water-repellent surfaces have generally been plant-based, like lotus leaves,” said Lin Wang, a doctoral student in the Department of Materials Science and Engineering at Penn State and lead author of the paper. .
Classical engineering theories have used this approach to create superhydrophobic or water-repellent surfaces. Traditionally, they are made with low solid fraction textures, which maintain an extremely thin layer of air above a low density of microscopic hair-like nanostructures, which researchers compare to an air hockey table.
“The reasoning is that if the drop or object is floating in that air, it won’t stick to the surface,” said Tak-Sing Wong, professor of engineering at Wormley Early Career, associate professor of mechanical and biomedical engineering, and Wang’s adviser. .
Because it works effectively, artificial coatings tend to mimic the low density of these nanostructures.
However, this document details a completely different approach. By examining surfaces such as a mosquito’s eye, the body of a springtail, or a cicada’s wing under high-resolution electron microscopes, Wang discovered that the nanoscopic hairs on those surfaces are denser, which is known in engineering as high solid fraction textures. Upon further exploration, this significant deviation in plant structure may impart additional benefits to repel water.
“Imagine if you had a high density of these nanostructures on a surface,” said Wang. “It might be possible to maintain the stability of the air layer from higher impact forces.”
This could also mean that more densely packed structures can repel faster-moving liquid, such as raindrops.
While the design concept is new to humans, the researchers theorize that this nanostructure increases the resistance of the insect in its natural environment.
“For these insect surfaces, repelling water droplets is a matter of life and death. The impact force of the raindrops is enough to take them to the ground and kill them, “said Wang.” So it is really important that they stay dry, and we found out how. “
With this knowledge drawn from nature, researchers hope to apply this design principle to create next-generation coatings. By developing a water-repellent surface that can withstand faster movements and higher impact drops, applications are plentiful.
From small flying robotic vehicles like drones Amazon hopes to deliver packages to commercial aircraft, a coating that can emulate these insect surfaces could provide greater efficiency and safety.
However, in light of the COVID-19 pandemic, researchers have realized that this knowledge could have an additional impact on human health.
“We hope that, when developed, this coating can be used for PPE. For example, if someone sneezes around a mask, those are high speed drops. With a traditional coating, those particles could adhere to the surface of the PPE, “said Wong. “However, if the design principles detailed in this document were to be adopted successfully, they would have the ability to repel those droplets much better and potentially keep the surface germ-free.”
As seen in this paper, the Wong Laboratory for Nature-Inspired Engineering extracts ideas from biological phenomena to make humanity’s innovations better and more effective.
“While we didn’t envision that application at the beginning of this project, COVID-19 made us think about how we can use this design principle to benefit more people,” said Wong. “It is up to us as engineers to take these discoveries and apply them in a meaningful way.”
The next step in this work will be to develop a large-scale, cost-effective method that can manufacture a coating to mimic these properties.
“In the past, we did not have an effective surface that could repel water droplets at high speed,” said Wong. “But the bugs told us how. There are as many examples as this in nature; we just need to learn from them. “
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Reference: July 17, 2020, Progress of science.
This research was funded by the National Science Foundation, the PPG Foundation, the Wormley Family Early Career Professorship, the Covestro-sponsored Humanitarian Materials Initiative Award and the Materials Research Institute at Penn State. Additional contributors include Ruoxi Wang, an undergraduate student, and Jing Wang, a Ph.D., both in the Department of Mechanical Engineering.
